Both sides of the major diplomatic incident sparked by Israel's decision to storm the Gaza-bound flotilla are invoking international law to condemn the others' actions.

Israel had vowed to block the flotilla from entering Gaza since last week, accusing the boats of embarking on "an act of provocation" against the Israeli military, and that its entry into the 20-nautical mile closure of the sea off Gaza would amount a violation of international law.

But there is mounting criticism that Israel breached international standards and human rights law through its use of armed force to storm the vessels.

International human rights law protects the right to life, and United Nations standards on the use of force and firearms by law enforcement officials set strict guidelines on the response by military and police in law enforcement situations.

Under the international basic principles, the use of violence is prohibited unless it is strictly necessary, and the use of lethal force can only be justified in self-defence or to protect life.

"We consider this a situation where once the Israeli commandos boarded the ships, and where they had effective control. These international standards are how a state is meant to respond to any acts of violence in a law enforcement situation," said James Ross, Legal and Policy Director at Human Rights Watch. "We are calling for a credible and impartial full investigation of the incident by the Israeli authorities."

Although competing accounts persist as to whether there were any arms on board the flotilla, and Israeli spokespeople have insisted that the attack was an act of self-defence.

But international law also requires that any use of force is proportionate, something that other states have already begun calling into question. Yesterday French President Nicholas Sarkozy said French President Nicolas Sarkozy condemned "the disproportionate use of force" against the flotilla.

Questions have also been raised about the violation of international maritime law by Israel's actions, after reports that the flotilla was around 80 miles from Gaza's coast when Israeli commandos boarded.

The position of the vessels in waters regarded as "the high seas" raises the prospect of an action for piracy and other violations of international law.

Although there remain competing definitions of piracy, it is defined by UN Convention on the Law of the Sea as illegal acts of violence or detention on the high seas outside the jurisdiction of any State.

Israel has already argued that its actions could not be regarded as piracy because it did not commit any crime when boarding the vessels, and experts say that government vessels are exempted from piracy claims, discounting legal challenges based on the use of military boats to intercept the flotilla.

The incident also places renewed attention on the blockade of Gaza, which has itself been described as a breach of article 55 of the Fourth Geneva Convention, which prohibits the use of collective punishment.

Last year the report by international judge Richard Goldstone gave both sides in the conflict three months to show they were willing and able to undertake investigations that met international standards.

Hamas has still failed to investigate, and a recent report by the Israeli military has been heavily criticised for failing to comply with international standards. Although the UN human rights council referred Goldstone's report to the General Assembly for follow-up, it has never reached the Security Council for possible referral to the International Criminal Court.